Size testing system



Feb. 20, 1940.` A. E.' GLANCY l sIzE TESTING SYSTEM Filed April 16, 19373 sheets-sheet 1v LNVENTOR /mva EsrELLE @Ln/#CY i fomuvEy Feb. 20,14940. l A E, GLANCY 2,191,107

` SIZE TESTING SYSTEM Filed April 16, 1957 l 3 Sheets-Sheet 2 fi El KVK?/Z 8^ N igll INVENTOR HMV/9 E5 TEL/,E mNcY Feb. 20, 1940. A E, GLANCY2,191,107

SIZE TESTING SYSTEM Filed April 16, 1937 3 Sheets-Sheet 5 INVENTOR` HmmEsrE/.LE Gui/#cy RNEY trate my invention: e

Patented Feb. zo, 1940 N UNITED STATES I V2,191,107 N f 1A1E1\111oFFlcE.4 o

"slzi: TESTING SYSTEM e e Anna Estelle Glancy, Southbridge,1 Mass., as-

signor to Americani Optical Company,Southv bridge, Mass., a voluntaryassociation of Massachusetts Application April 16, 1937seria`1 No.137,229

3 Claims.

`'llfie present invention relates to the measurement of themagnification producedby an optical system,` and more particularly toimproved method and means for varying the sizeof image 1 @Vobtained by alens lin a lens measuring device without change in the focal power ofthe system so as to accurately determine the magnification attributableto the lens.

cided advantages as applied tof a lens measuring device of the typedisclosed in Troppman Patent A No. 411,083,309, patented Januaryj, 1914,and the invention will, forwpurposesV of illustration, ybe 1 "describedand shownas applied to `such a lens .e 1. meauing device. It will beunderstood, how- 1 "ever, `that my invention may beapplied to` other edevices where it is found `desirable to change the image size.

Wln the accompanying drawings which illusuring device shown inFig. I;

1 26 tion of optical systems foundin the lens measlFig. `III is asectional View taken on line IIl--II` "of Figo. I and looking in thedirection indicated by the arrows;

Fig. 1V is an enlarged in side `elevation of 1 e 1the optical systemincorporated in the lens meas- `uririgdevice for determiningmagnification, this `optical system being such that the separation ofitself-ments can be varied to determine the mag- Ariiiicati'onattributable to 4alens being measured;

1 Fig. V is an end view of the mechanism shown inFig. 1V, this viewbeing taken from the right end of Figi IY;V

`lig. VI isa partial detail view showing the image of the targetappearing in the focal plane of the focusing system or objective lenssystem of the lens measuring device; e, 1

` Fig. VII isa' similar detail view showing this y image as `thrown upon`the screen andviewed thr`ough the eye piece` `of the lens measuringdevice; e e e Fig; VIII is a horiaontalsectional view through the eyepieceand screen of the device, the plane `of1 this section passingthrough the axis of the eye piece; 1 e

e Fig. `TX is a fragmentary view illustrating on 1van enlarged scale theadjustable nose` of the lens measuring device; e 1 e .e 11 Fig. X is adiagram similar to Fig. II of a modication of the arrangement of opticalsystems in ,1, The novel principles of my invention have de- 1 which anelement of one system ismerged in an adjacent system; and

, Fig. XI isa diagram similar `to Fig. II modified to take care ofmeasurements of reciprocal magy nication inrcorrectivle lenses` for nearvision. 5

Mechanism kand a `technique for determining e the difference in theangular size of the ocular images of the two eyes of a patient aredescribed in the application of Kenneth N. Ogle, Serial No. 713,701filed March 2, 1934,` The prescription 10 lenses having been prepared,it becomes important to be able to exactlydetermine the magnificationproduced by these lenses. 1 j 1 Accordingly one object of my inventionis to provide means'for acurately measuring the mag- `nication producedby a lensor lens system. A

further object is to provide an attachment for a lens measuring devicefor determining the magnification attributable to the lens `beingmeasured. y f 1. 2U

Referring `tolthe illustrative embodiment of my' invention shown inFigs. Iand II thelens meas-` uring device includes a combination ofoptical systems Whose members are indicated by letters.

A projection lens system C` transmits ythe light 25 from `a target D,and can be focused so as to pass the light as parallel rays :through alens rest B. The target D receives illumination from an elec- 4triclight `bulb EL If desired, a condensing lens `or lens system may,v beinterposed between the 30 bulb' E `and the "target D for obtaining`better i illumination of the latter.` A lens F to be tested or measuredis shown held inplace on the nose or lens. rest B. e

A1The parallellight rays, after passing through 35 the lens rest B, passthrough the variable size system Gto which the present inventionemoreparticularly pertains;` and are thenfocused 0n thescreenH provided witha screw J for centering the screen so `as to accurately receive the 40image vofthe target D. The lenssystemufor thus focusing the image on thescreen H is indicated atl K; and `is designed softhat parallel light isfocused by this lens system K in the plane of the `screen H. The screenI-I is viewed by the observer rest B; the carriage N `must be moved` tochange B6 v j' power of the klens on'the rest B. y

the distance from the target D to the lens system C in order to againbring the image of the target D into sharp focus on the screen H.Thelens F on the lens rest B being at the principal focus of the lenssystem C, the scale P is a linear scale, i. e. if we consider :c to bethe linear displacement of the target from its zero reading, which is atone of the yprincipal foci of C, and :cf to befthe ,distance ofthe imageof the targetfromithe' other principal focus of C, and f to be the EFLof C,

then the relation holds true that x.:c=f2; and...

when the lens or optical system F under ytestis placed on the rest B,the linear displacement"Y face of F which is at a principal focus 'ofVC.. `The reading on the scale P therefore gives ,the focal In theembodiment shown, the `carriage slides along a table 5, andhas a rack'lsecured `to its under side which is engaged bya pinion 8 which may be`manipulated througha dial 9 rotatable j therewith. The outer peripheryofthe dial has suitable graduations F which, in 'cooperation with ,anindicator I I, indicate rthe power in diopters' of the lensF beingmeasured. i

` v The projectionA lens system Cis mounted in a tube I3 suitablysecured in the upper end of an apertured bracket I4. The lenspositioning nose or lens rest B Vis threadedly engagedly engaged in theforward end of the tube I3. This nose may be screwed in or out tozadjustthe position of -is moved -in theA groove rthe lens F so that thesurface in engagement with the "nose BY will be` exactly inrthe planevof the ,principal focus ofthe lens system C.` `When a lens 'or' lenssystem F to bel tested is placed on the nose B, the dial 9 maybeladjusted untila 'clea cut image of the Atarget D is seen'in the planeof ,the screen H. The reading of the dial,

'of course, indicates theA focal power of the lens for lens system.

v y Suitable means such as a gooseneck bracketIIi Vhaving an aperture I1through which the rays of vthe image may pass is operable tofbear in oneposition against the outer side` of 1the lens Fv being tested or toswing toinoperative position `for releasing the lens F.` The lower end-of `the bracket I5k is slidable in a tubular guide I8, and is biased bymeans of a spring (not shown)v so as `M, the lens system `of the latterbeing mounted (I0` for sliding adjustment relative to the support 24 soasto permit adjustment for thefocal'- requirementof each individualoperator. The slidef22 23 `byvmeans of an ad-` justing'screwJ. .l j

The screen Hrcarriezd bythe slide 22 is shown herein in ,the form of aplate or ltransparent rmember having opaque referencelines 241 thereonl(See-Fig. VII).` The target Dis' provided with ,The image viewingportion oftheinstrument alsocomprises a tube .30 in which is mounted the.focusing lens system K. This systemK is composed ofitwo' or more lensIelements which are so Ainto conformity therewith.

mounted as to be adjustablefor bringing the image of the target D uponthe screen H to such a size as to accurately superimpose the referencelines 21 upon the lines 28. I Such adjustment is made telescoping tube34in which the target D is mounted,the tube 34 being adjustable to permit:the alignment of the target D with the scale 35 at the time of assemblyof the instrument. V The scale 35 is on a dial 36, andcooperates with amarker 31 on the bracket 33. The target D can be rotated to orient thelines 28, and the marker 31 indicates on the lscale 35 the angularposition of th'ejlines28. v'Ihus theoperator has theselection ofrotating either thebox-like support. or thetube32 to` bring the lines 21and 28 into alignment; `and he ,mayl change the angularposition ofonefor some purpose and rotate the other The apparatus, as thus fardescribed, functions to focus a sharp imageof the target D on the`screen H. If` there is no lens F on the restB, f

vinstniment was correct. If a lens or lens system F is placed on therest B for..measurement`, the dial 9 is rotated tovagain'bring the imageof the A disclosure of suitable structarget D' on the screen H` to asharp focus, but` now .the lines r21 do not register accuratel'yhwiththe lines 28 due generally to what is described below as shapemagnification. However, if the lens or lens system F has some prism, thescrew J ,4.

lthe liens or lens system F.

The change in ther size of image introducedfby the lens or lens systemFll is measured vby corn"- Vpensating this change in size by thevariable size system G which is interposed between the lens F onthe restBV and the focusing lens systems K. The system G is adjusted to vary thesizeof im-v age until the lines 28 again exactly register with the lines21 onv the screen H. The separation between the middle lens and an endlens of lthe system, .gives the readings; and as mentioned .below therelation is linear, so that variation in size isl measured by a scale ofsubstantially equal intervals. The 'Variable size system `and rtheprinciples of the relative ,movements of its elements will now bedescribed. i v

As explained in my copending application Serial No. 131,352, filed March17, 1937, three lens elements I, II andIII can be adjusted in relativeposition so as to obtain a desired change` in magniiicationyand if thisis done by properlyv varying the separation of the three lensk elements,this change inmagnification can be accomplished withoutappreciablechange in focal power, i. e., without change in the sharpness ofimage ofthe target D on the screen H. f A

In the application of E. D. Tillyer, Serial No. 720,594, filed April 14,1934, is given an expression for the angular magnification of 4a distantobject by a lens -orlens system M'=S\P.Where S is a factor known asshape magnification dependtarget asseen through the-"eyepiece This in`dinitelythin 'lens would have no shape magnification; but when alenshaving substantial thickingcn all the surface` powers `except thelast refractive surface` (the.y one nearest the stop point and uponl`theroptical thicknessesand separations, 'but independenbofthetotalpower of ;the system and P `is a `factor known as 'power`magnification.depending on the total power of `theysystem andthepositionfof the stop.

`It willfbenoted` that in the lens measuring `device disclosed inthepresent application, the

focal power of the lens or lens system F has no effect on the size ofimage producedon the. screen Hr; In other words, the change in theposition of `:the target D relative `to.` the projection lens system Celiminates the effect of the focal power' of Fas concerns the size of`image seen through theleyepiece This meansthat when the lens supportingedge of rest B is exactly inthe focal plane :of projection system C,aninnitelythin` power lens placed against'this edge with the target Dadjusted for a `sharp focus on screen H would not change the apparentdimensions of the ness is placed against. this edge and the focal poweris compensated for by focusing the target D, the apparent dimensions ofthe target will be changed tothe extent-of the shape magnification S.`This gives the shape magnication SJ independently of `the powermagnification P' of `the lens F'. The relation 1Vr ":`=S P', or ratheris the basis` of my equations,` and Iv find it more convenient-.tointroduce'the following notation;

Then .zcr..=s.1 .l d d The required movements of the lens elements I, IIand III lwhich will 'give rigorously the desired changesin magnincationwithout change in focal power aref determined by the followingequations: i

D1, D2, D3, D4, D5 and Ds are the surfacepowers of the three lenselements in the order beginning with-the surface nearest the objectivesystem K;

si, s2, s3, s4, and S5 arethe optical thicknesses and separations;

- Dimm is the feifective power of the partial system II-l-III. i i ADmis the additive power of lens III with respect to lens II, i. e.,thepower of lens III which `is additivetolensII inthe sense used in anadd ditve trialfset; i

Mplis the reciprocal of the factor which we are here determining; and

l Equation l.

AMI, is a finite change in li/lip. l is the condition for a constantbackfocal length, or in other words\,.for constant focal pcwelt?Equation 2 givesthe scale value for change in Mp fora givenmotion oflens elements II and III; and as Mp changes in direct power of thissystem is zero. t

proportion to the change in separation between lensesill and III,the-"scale on which reciprocal magnification is read is linear. Inthisdiscussion it has. been assumed that the lens element I is fixed andthat the lens elements which are moved `are lens elements `II and III.Butas both the entering and the emergent rays are parallel; lens elementIII can be fixed while lenselements I and I are moved. i iMorecver,` aspointed out in my copending application above identified, the focalerror caused by maintaining both outer lens'elements, namely I and III,stationary is insignificant in a vsystem which is well designed for thispurpose. The best arrangement of which? I am aware is one in which themiddle lens element II is negative, the two outer lens elements beingpositive and of substantially equal power. f `For measurements ofreciprocal magnifications up to i5% the following system gives goodresults. It will be assumed that is given compensating movementasrequired by the Equations 1 and 2 given above, the scale is dividedinto intervals' 2 imm. `in length, each intervalvrepresenting y1%magnification. Y

If both outer lenses are .maintained stationary,

the scale indicating `the reciprocal magnification `is changed `tocompensatethe error thusintroduced; solthat on the minus side of thescale each 2 mm. interval is equivalent to 0.975% instead of 1%, whileon the plus side each 2 mm. interval is equivalent to +1025 The centercfthisflensis 3.046 mm. thick.

`I will` now` give a speciiic example'whichis usable for, reciprocalmagnications up to i 10%. Again it isassumed that the index ofrefraction is lenses is plane and the'othersurface of each is convex.The radius of the latter surfaceof lens I is 219.83 mm.` or apowerof2.380 diopters, and the radius of this surface of lens III is 220.30 mm.of a power of 2.375 diopters; and the thickness of both `lens I and lensIII at the center is 1.904 mm.

The radius of each of the surfacesof the negative i middle lens is209.08 min. or a power of w2.5024 diopters, the center being 11.523 mm;thick. The

Assume that either lens I or lens III is fixed. The middle lens II ismoved along a scale in which each interval is 2 mm. long and represents10% magnification, the movement taking place in either direction fromtheV approximately central position at. which magnification is unity. Asbefore, if lens II is moved to the right (toward lens III) along thescale, there is a decrease in size of image; and if` moved to the leftA(toward lens I) there is an increase in size-of image.` At the zero.-setting, in which the adjacent surfaces `of lens I` and II are separatedby 20.80 mm. and the adja'" cent surfaces `of lenses I andvIII by 21.00mm., the separation of thetwo-plane (outer) surfaces of lenses I and IIIis 47.14.1nm. If `the middle lens IIis moved tothe right to the +10%position,` the separation of these two plane (outer) surfaces. changesto 45.43 mm., while thefsepara- "1;5232. The `outer surface of each ofthe outer Vtions betweenthefadjacentf surfaces? ofan'd' II,

and-II fand `IIIfV'becorne- 39 ;09- mm. vand 1.00 mm.

eachfl%f change in reciprocal magnification would correspond tol'.9l2"mm.'or in otherwords 2 v'm'm; would correspond to 1.046%reciprocal magr'iication.v

In theseexamples the middle lens II is negative and the outer lensespositive; however, it 'will be u'nderstood'that` the middle lens II maybe positive and 'thev outer lenseslnegative, the symmetrical arrangementof the outer lenses beingpreferably retained. Thissymmetricalarrangement in which the outer lenses are of substantially thesame'power is conducive of minimum error due to maintaining both outerlenses stationary and movingv only the middle lens. 1

Thepower of the middle `lens-determines the size of interval onthe scale'corresponding to a change of '1% `inreciprocal magnication. i

The mathematical basis ,for the `above is given in my' copending`application above identified.

' "'Fro'm' the;` above itwill benotedthat the scale on which .reciprocalmagnification is read is linear; It ish'als'o true that the equationrepresentingtheirequired-movernent of the lens element vIII is `ofthesecond degree, and its curve is asymmetrical parabola with a vmaximum atthe zero position of the middle lens, i. e., with magnincation unity.

In my copending applicationjabove identified, I" have illustrated anddescribed `a device for bringing about the requisite correlatedmovements of lenses II and III. For measurements 'of reciprocalmagnification which must be rigorously exact, a device which will bringabout these movements of the middle lens'element and one of theend-flens elementsmust'be employed. For the purpose ofmeasuringophthalmic lenses .prescribed for the correction of abnormalconditions as to size and shape of theA ocular'y images ofthe twoeyes-known as"aniseikonia, itis possible touse a well'designedl systemof lenses of which only the middle lensis moved. Mechanism for moving'the middle lens of such arsystem is illus-r trated more particularly inFigs. I, IV and V of the present application. v

i. A" lens cell `39 is secured on the end of the tube 30 nearesty thelens -rest B. By means of this cell the lens element I'is carried inYfixed relation to the focusing system The remaining two elements of thesystem G are carried by ay frame .4I mounted on the Vcell`."s9. 'A cell42 carrying the middle lens II has an outer annular .portion 43perforated to receive thethree post`s145,l46 and 4l oftheframe'M. -Thepost 41 isthreaded to cooperatewitl'i a micrometer nut y49 on theperipheral portion 43. The graduations are markedon the'post 45: thesegraduations correspond tothe pitch of the screw thread on the pest 4l sothat-one complete rotation of the nut dadv'ances the lens cell 42 andits peripheral portion 43 exactly one graduation on the post 45.A

-The lnut 49-.isl marked-==withfgraduationscooperat- Vingwith armar-keron the 'portion 43l so as to'indicate` tenthsy y of turns "oflf thenut-19. The outer portionof the 'nnut`Y 49 Imayfbe-fknurledforcenvenience `in `turning* the .-nut. 'In' orderj to .insure alignmentof' the zaxis oftheA ylenselements II durf ing itstravel, sa' sleeveportion 50' extends `from theiperipherall portion f43along"thevpost 4lto provideanrelongatei'bearing for `the latten-*1A y"colla spring..i5l:is interposed-'between theperiph-` eralaportiona'andthe end-of thefframe4I oppositefthe `nut .49 :so: as-to takeup' slack-and give moreY*accurate readingsioff 'the micrometer? nut.

" LensfelementfIII-is mounted in a lens cell 53` adjustably.` supported1in the fend fof vthe frame 4| opposite `the* cell 39." A vpin`54 xed toa sleever .55 extendsv intoa' cam slot 56 in the cell 53,

. whereby slight adjustment of the position ofv lens elementslIrelativeto' lens element I may be effected.` "Ihesleeve 55isiixed` onthe end of the `of adjustment of .thecell 53. f

The mechanism illustrated in Figs. 1v andr v isfsuchzthat theopticalsystem Gis 'detachable from the. lens y"measuring 'device'. J'It' isdesirable in some cases that this'lens system G be an attachmentzwhichis putin position when required and removed whenanot'used.`v In othercases it is desirable that the lens system G be a permanent part of thelens-measuring device; and as it in ra separatey lens cell1 39,it isadvantageous to incorporate the lens element I in the objective lenssystem K. Accordingly, this lens element loses its separate identity,and the lens system K is not necessary then tocarry the lens element Iis so calculated as to have bothjits own function and the function oflens element I of system G.

A modification of the combination of optical systems'by whichthismergingvis carried out is illustrated'lin Fig. X. Here the objective lenssystem K ismadesomewhat more powerful than` 1n the combinationof Fig;II, since the light entering K is divergentinstead of parallel. rIny ofthe'system K, account will of course be taken of the poweradded whenlens element I is merged` in system K. The separation s2 is heremeasured of this negativel lens, the zero setting of the target Dv hasbeenk shifted. Furthermore, the light entering the auxiliary lens R isconvergent. The

, lens R serves to render this convergent light parallel before enteringthe objective lens system K. The power of the minus lens R required todothis and: its .location relative to thelens rest B are determined by thecondition that its virtual computing for correction of sphericalaberration focal plane is at such distance from the lens rest g B as hasbeen assumed as standard reading dis-v tance, in general about 400 mm.-4The image of the target, as seen in the eyepiece M, is largerthanthe'image seen in a lens measuring device when arranged according tothe diagram shown in Fig-II; ,and accordingly the screen H' used in thearrangement shown in Fig. XI must be thus 5 face of a` spectacle` lensor lens system. If the near vision zero setting ofthe lens measuringdevice is -`-2.50 on the scale P, the near vision object distancemeasured from the ocular surfaceyof spectacle lens (or from a point13.75`

l mm. fromA the cornea) is 400 mm. This is arbitrary.

`Between the auxiliary lens Rand ther lens rest B is inserted a threelens system G designed for near vision according to the principle setforth in l my copending application` above identified. As

taught `in that application, a near vision system is designed for aspecific object distance u1, meas-l ured from. the object tothe lens'element III. Here the`object distance u1 is the distance (f1-4Z) zofrom the image T to the lens element III. Ac-

, `cordingly the required near vision system can be designed for thisspecific object distance and located with the xedlens III in suchposition that they vergenoy of the light for `near vision measurementsand the design of the near vision sys- Since `the near vision three temare consistent. lens system is terrascopic, the vergency of the q lightis not altered by passage through the system.

0 Thexrequired movements of` thelens elements,

I and II which will give the desired changes in magnicationwithoutchange in focal` power are here determined by the following equation:

i.` e., the same image position results whether an object at nitedistance u1, is refracted at the surface D6, or an infinitely distantobject islas-d sumed to be refracted at a fictitious' surface 3 are theequivalent powers of lenses and II) respectively.

By denitiomequivalent power is the reciprocal of the focal lengthreferred to the principal planes of a lens or a system of lenses. Thismat- 5 ter is fully disclosed in my copending application Serial No;131,352, filed March 17, 1937.

It is not always necessary, however, to obtain such rigorously exactmeasurements. A workable system is provided if lens II is kept fixed.

i In such a modified arrangement, the system. de-

parts from the terrascopic condition slightly, and this error can becompensated by appropriate adjustment in the scale value by whichreciprocal magnification is indicated. `The correction in` the salereading is equal to a factor times `the terrascopic magnification andthis factor is where `11, theoretically is the distance from the stop`or window to the object, and actually is approximately the distancemarked f1 in Fig. XI.

The arrangement of optical systems, illustrated in Fig. XI, are operatedas follows: 'I'he target l D of the lens measuring device is moved tothe properse'ttin-g on the scale P` to give a sharp image of this targeton the scale H. It is immaterial Whether the optical system. G' is inpo-i sition or not at the time when the image of the target is` focusedin they eyepiece, since the sysyk tem G is terrascopic. The zeroreadings of sys'- tem G" gives unit magnification. The near visionlensfF to= be measured is positioned on the lens rest B1 with itsbou-lar surface `against the lens rest. "Ihe target' D is shifted untilthe image is again `seen sharply in the eyepiecev M. If there ismagnification, the lines 2l and 28 do not acci-irately1l register. Whilethe image remains1 sharply in focus, the' lines 21 and Z8 may be broughtinto registryby shifting lens I (or bothf lens I and lens II `forrigorously accurate determinations). .When by suchoperation of theoptical system `G the linesZ'l and'28 have been brought into accurateregistry, the per cent magnification Iis read from the reciprocalmagnification scale.

` lensto` be Worn at a different distance, a correo--l `tion must beincorporated in the power of lens prescribed. A lens measuring deviceequipped withfa movable lens rest, such as illustrated in Figs. I and IXof the present application, affords a means of measuring directlywhether the lens or lens system will have the same effect on the eyeasthe `original triallens, when worn at the prescribed distance from thecornea. Also, such a movable lens rest can be set for the prescribed'`change of position toldetermine the amount by' which the prescriptionshould be changed. As illustrated in Fig. IX,`the lens rest B is movableinand out from its zero setting, that is, the position wherein its lenssupporting edgelies in the plane ofthe principal focusof the projectionlens system C. To determine this zero position and to determine' theamount of in and out movement of the` lens rest B, suitablel scale andindicator" means `60 and El arey used'. The lens rest B is threaded intothe tube |3` according to the em` an adustable `lens rest of the typeillustrated in` liig.` IX,for measuring the magnification produced by alens when Worn in the prescribed position, for instance, at a differentdistance from the cornea thanthat atwhich the trial lens was placed.Moreover, it 'sometimes happens in the designing of lenses forcorrection of the difference in the angular size of the ocular images ofthe two eyes that the tWo lenses are designed to be' Worn at differentdistances from the cornea. By employing a size measuring system G or G'(as the1 case may be) in cooperation with an adjustable lens rest B,itis possible to verify the p lenses furnished to the patient.

The teaching of the present application relates primarily toimprovements in the determination.,

' it accurately registers with the reference lines or i are of coursepossible.

not. YThis contributes toward more accurate observations, particularly.with a somewhat less experienced observer. n u

I In. explaining my invention I have given certain specic examples Mbythe way of specific application of the 'principles of myv invention.Variations in the applications of these principles not stop atf5%, or10%',-if larger magnications are desired. Moreover, although I havegiven examples which start from a zeroposition,it will bevobvious thatinstead of starting from zero it is quite as feasible to design a systemfor which n the magnification yat the zero position is different fromunit. It will be understood, therefore, that my invention is not`limited `to the specific ex` amples given but may beotherwise embodiedand 'practiced `within the scope of the following claims.

1. A device for measuring the shape magnication of a lens systemcomprising a test target, a projection lens system normally so locatedrelative lto saidtest target and having suchoptical characteristics asto producey a projected test image of said testtarget by parallel lightema- 'nating from said system, ymeans for supporting a i0 lens system tobe tested at a test position located substantially at l a principalfocal point of said projection lens system whereby the parallel raysemanating from said projection lens system -will traverse said testposition,`means for moving said test target toward and away from theprojection lens system an amount su'icent to compensate fory deviationsof the light rays from parallelism as eifected by the focal power of alens system` under test and located at saidtest position .so that saidrays will emanate from said lens system under test in substantiallyparallel relation simulating the parallelism' of said rays as normallytraversing said test position, means for receiving the image projectedby saidrays having size scale indications of azero size image associatedtherewith and means including a lens system for shifting the` width ofparallelism ofthe rays to increase or decrease the size of image whichis projected by said parallel rays after traversing the lens systemunder test, with substantially no introduction of focal power, until thesize of v'image simulates the width of the zero size image scaleindications and means vgraduated in terms of percent magnification andassociated with said 3lens system for altering the size of the image forindicating the extent of adjustment necessary to produce an image of thesize of the zero size'image of thescale indications.'

The magnification need i 2. A device formeasuringztheshape magnificationof alens system for use with an instru.-v ment vhaving a test target, raprojection lens system normally located relative to said test target andhaving such optical characteristics as to produce a projected test-imageof said test target. by parallel raysvemanating from said system, meansfor supporting a lens system to be tested;,at a

test position located substantially `at a principal focal point of' saidprojection lens system whereby the parallel rays emanating from saidprojection lens system will traverse said test position, means formoving said test target toward and away from the projection lens `systeman amount sufficient to compensate for deviations of the light rays fromparallelism as effected by the `focal `power of `a lenssystem under testand located at said test position so that said rays will emanate fromsaid lens system under test in substantially parallel relationsimulating the parallelism of said rays as normally traversing saidtest` position, said device for `measuring the shape magnificationcomprising a lens system of three lens elements whose opticalcharacteristics may be variedfor increasing or decreasing the width ofparallelism of the rays to increase or decrease the size of image whichlis projected` by said parallel rays after traversing the lens system`under test, with substantially no introductiony ofl focal power, to varythe size of image to render itsubstantially equal to a predeterminedzero size of image and graduatedmeans associated` with thelens system ofsaid device for indicating the extent of adjustment necessary to producean image of the size of the predetermined zero size image, and meansassociated with said instrument on which the image may be focused for'sizing.

3. A device for measuring the shape magnification of a lens systemcomprising a test object,

`a projection lens system, means for positioning the lens system to betested at one of theprincipal focal points of said projection lenssystem,V

meansforlviewing said image, av focusing lens system for bringing theimage of said test object projected by said lens system to a focus onsaid means for viewing said image, means for adjust-'f ing said vtestobject relative to said projection lens system, scale means cooperatingwith said test object and having its zero pointat the conjugate focaly point lof said projection lens system so that `light rays emanating fromsaid projection' lensl system'will normally be substantially parf allelWhenthe test object is at Vsaid zero point,

saidy testl object being 1 adjustable toward and`v away fromtheprojection lens system to com;

pensate for deviations of the vlight rays from parallelism as'effectedby the focal power of va lens system under test located at said liirstnamed principal focal point of said projection lens system and acalibrated optical system, disposed be` tween the focusing lens systemand the lens system to be tested when in said test position in saidinstrument', and capable of adjustment to optically vary the dimensionsof the projectedy image without appreciably varying the plane of saidimage;

ANNA ESTELLE GLANCY.

